1. Field of the Invention
This invention relates to a composition which cures to an improved flame retardant silicone rubber and to methods for making such a composition and rubber.
2. Description of the Prior Art
Silicone elastomers have various superior properties, but they suffer the drawback of being flammable and various methods have been proposed for making them nonflammable. As a representative example of these methods, a method is known from Noble et al. In U.S. Pat. No. 3,514,424, issued May 26, 1970, in which a platinum-containing material is combined with a silicone rubber compound. However, since a platinum-containing material alone does not impart sufficient flame self-extinguishability, many studies have been conducted on improving the flame extinguishability by combining the platinum-containing material with other compounds. For example, Laur et al. in U.S. Pat. No. 3,635,874, issued Jan. 18, 1972, teach a combination of a silicone rubber composition containing a platinum compound and fumed titanium dioxide. Itoh et al. in U.S. Pat. No. 3,936,476, issued Feb. 3, 1976, teach a combination of a silicone rubber composition containing a platinum compound and powdered manganese carbonate; and Hatanaka et al. in Japanese Patent Publication No. Sho 51(1976)-35501, published Oct. 2, 1976, teach a combination of a silicone rubber composition containing a platinum compound and (FeO).sub.x (Fe.sub.2 O.sub.3).sub.y where the ratio of x to y in the formula is 0.05/1 to 1.0/1; Harder in U.S. Pat. No. 3,652,488, issued Mar. 28, 1972 teaches a silicone rubber composition containing carbon black and a platinum compound; and Laur in U.S. Pat. No. 3,996,188, Dec. 7, 1976, teaches a silicone rubber composition which contains an alcohol producing organic peroxide, platinum, an aromatic acid, and an additive selected from titanium dioxide, carbon black, Group II metal oxides, rare earth metal oxides, and rare earth metal hydroxides.
However, those known methods do not produce a satisfactory flame self-extinguishability. The combination with a platinum compound and fumed titanium dioxide degrades the electrical properties of the silicone elastomer due to moisture. The combination with a platinum compound and manganese carbonate interferes with vulcanization and prevents sufficient vulcanization when an acyl organic peroxide is used as the vulcanizing agent. The combination with a platinum compound and (FeO).sub.x (Fe.sub.2 O.sub.3).sub.y shows a rather weak flame self-extinguishing effect unless the amount of addition is large. However, when the amount of (FeO).sub.x (Fe.sub.2 O.sub.3).sub.y is increased, the mechanical properties of the silicone elastomer deteriorate and, furthermore, it causes a reddish brown to brownsih black coloring of the elastomer to the extent that the elastomer becomes impossible to change to another desirable color.